A. J. Rostocki

New ultrasonic Bleustein-Gulyaev wave method for measuring the viscosity of liquids at high pressure

In this paper, a new method for measuring the viscosity of liquids at high pressure is presented. To this end the authors have applied an ultrasonic method using the Bleustein-Gulyaev (BG) surface acoustic wave. By applying the perturbation method, we can prove that the change in the complex propagation constant of the BG wave produced by the layer of liquid loading the waveguide surface is proportional to the shear mechanical impedance of the liquid. In the article, a measuring setup employing the BG wave for the purpose of measuring the viscosity of liquids at high pressure (up to 1 GPa) is presented. The results of high-pressure viscosity measurements of triolein and castor oil are also presented. In this paper the model of a Newtonian liquid was applied. Using this new method it is also possible to measure the viscosity of liquids during the phase transition and during the decompression process (hysteresis of the dependence of viscosity on pressure).

Application of SH surface acoustic waves for measuring the viscosity of liquids in function of pressure and temperature

Viscosity measurements were carried out on triolein at pressures from atmospheric up to 650 MPa and in the temperature range from 10°C to 40°C using ultrasonic measuring setup. Bleustein-Gulyaev SH surface acoustic waves waveguides were used as viscosity sensors. Additionally, pressure changes occurring during phase transition have been measured over the same temperature range. Application of ultrasonic SH surface acoustic waves in the liquid viscosity measurements at high pressure has many advantages. It enables viscosity measurement during phase transitions and in the high-pressure range where the classical viscosity measurement methods cannot operate. Measurements of phase transition kinetics and viscosity of liquids at high pressures and various temperatures (isotherms) is a novelty. The knowledge of changes in viscosity in function of pressure and temperature can help to obtain a deeper insight into thermodynamic properties of liquids.

Employment of a novel ultrasonic method to investigate high pressure phase transitions in oleic acid

In this work, the variation of sound velocity with hydrostatic pressure for oleic acid is evaluated up to 350 MPa. During the measurement, we identified the phase transformation of oleic acid and the presence of the hysteresis of the dependence of sound velocity on pressure. From the performed measurements, it can be seen that the dependence of sound velocity on pressure can be used to investigate phase transformations in natural oils. Ultrasonic waves were excited and detected using piezoelectric LiNbO3(Y-36 cut) 5 MHz transducers. The phase velocity of the longitudinal ultrasonic waves was measured using a cross-correlation method to evaluate the time of flight.

An application of Love SH waves for the viscosity measurement of triglycerides at high pressures

A new ultrasonic method of viscosity measurements at a high-pressure conditions has been presented. The method is based on the Love wave amplitude measurement. The same electronic setup as in the Bleustein–Gulyaev (B–G) wave method applied by the authors recently for a high-pressure measurement was adopted. The new sensors were made of metallic materials, which make them more reliable at high-pressure conditions. The method has been successfully applied for the viscosity measurement of some triglycerides at high-pressure conditions up to 1 GPa. The results have been compared with the earlier results obtained using B–G waves. This comparison has shown that Love wave method sensors are more reliable than B–G wave sensors and are also cheaper in fabrication, although the sensitivity of Love wave sensors is lower. During the measurement, the phase transitions in the investigated liquids were observed.

Determination of physicochemical properties of diacylglycerol oil at high pressure by means of ultrasonic methods.

The purpose of the paper is to address, using ultrasonic methods, the impact of temperature and pressure on the physicochemical properties of liquids on the example of diacylglycerol (DAG) oil. The paper presents measurements of sound velocity, density and volume of DAG oil sample in the pressure range from atmospheric pressure up to 0.6GPa and at temperatures ranging from 20 to 50°C. Sound speed measurements were performed in an ultrasonic setup with a DAG oil sample located in the high-pressure chamber. An ultrasonic method that uses cross-correlation method to determine the time-of-flight of the ultrasonic pulses through the liquid was employed to measure the sound velocity in DAG oil. This method is fast and reliable tool for measuring sound velocity. The DAG oil density at high pressure was determined from the monitoring of sample volume change. The adiabatic compressibility and isothermal compressibility have been calculated on the basis of experimental data. Discontinuities in isotherms of the sound speed versus pressure point to the existence of phase transitions in DAG oil. The ultrasonic method presented in this study can be applied to investigate the physicochemical parameters of other liquids not only edible oils.

On the improvement of the metrological properties of manganin sensors

The paper presents the recent progress made in the accuracy improvement of the manganin pressure sensors at the Warsaw University of Technology (WUT) and at the Institute of Nuclear Energy. The efforts of the authors were concentrated on three problems: The improvement of the temperature characteristics by the design of a manganin sensor with the temperature compensation achieved by the application of two manganin coils with two different temperature characteristics; The improvement of the calibration process by using a high pressure deadweight piston gauge (with the correction of effective area versus pressure dependence, built at WUT), measurements of the manganin resistance as a function of the temperature and of the pressure using a precise multimeter and application of statistical methods for long series of measurements. The modification of the thermal characteristic by implantation of bismuth and krypton ions.

A viscosity measurement during the high pressure phase transition in triolein

The high-pressure properties of triolein, a subject of extensive research at the Faculty of Physics of Warsaw University of Technology (WUT) have been enhanced by the results of viscosity measurement within the pressure range up to 0.8 GPa. For the measurement the authors have adopted a new ultrasonic method based on Bleustein-Gulyaev waves, successfully developed earlier for the low pressures in the Section of Acoustoelectronics of the Institute of Fundamental Technological Research. The measurements have shown: 1. Exponential rise of viscosity with pressure up to 0.5 GPa. 2. Extraordinary increment of viscosity at constant pressure during phase transition. 3. Further exponential rise of viscosity with pressure of the high-pressure phase of triolein. 4. The pressure exponents of the viscosity of both phases were different (the high-pressure phase had much smaller exponent). 5. The decomposition of the high pressure phase due to the slow decompression have shown very large hysteresis of viscosity on pressure dependence.

Pressure-induced phase transition in soy oil

Following the earlier works [R.M. Siegoczyński, Reports of the Institute of Physics. No. 46, Publishing House of the Warsaw University of Technology (1998). R.M. Siegoczyński, J. Je¸drzejewski and R. Wiśniewski, High Pressure Res. 1 225–301 (1989).] on the investigation of oily liquids such as oleic and triolein, authors predicted the occurrence of a phase transition in the wide class of commercial oils containing oils with double carbon bonds. Those predictions have been confirmed by the observation of the phase transition in rapeseed oil [A.J. Rostocki, R. Wiśniewski and T. Wilczyńska, in press]. The present article shows further confirmation of those predictions presenting first-order phase transition in soy oil. The measurements performed in the range up to 1 GPa have shown pressure-related discontinuity of permittivity and volume.

Certain physico-chemical properties of triolein and methyl alcohol–triolein mixture under pressure

The article discusses further research of the new high-pressure phase in triolein and in triolein mixed with methyl alcohol. The transformation from the initial isotropic state of liquid to the high-pressure phase in case of the mixture of triolein–alcohol was observed by us for the first time. In this study, we compare the phase transformation under pressure, both for oil and for oil–alcohol mixture. Spectra of Raman and UV–VIS absorption show that the application of pressure to triolein leads to partial irreversibility of the observed processes. That partial irreversibility is important for the food conservation methods based on high-pressure technology since triolein is a good model of the most of vegetable oils components.

Observation of pressure-induced phase transitions in rapeseed oil with methyl alcohol mixtures

A high-pressure research on rapeseed oil and mixtures of rapeseed oil with methyl alcohol has been made. In all cases, at least one occurrence of the first order phase transition similar to that in castor oil was noticed [R.M. Siegoczyński, Reports of the Institute of Physics. No. 46, Publishing House of the Warsaw University of Technology (1998)]. Experiments were performed in a cylindrical chamber with a simple piston system, working together with 20 ton hydraulic laboratory press. The pressure in those experiments was approaching 1 GPa. Changes of pressure, volume, temperature and capacitance were recorded using an advanced data acquisition system. In this article, the changes of the relative electric permittivity ϵr as function of pressure and also the compressibility of investigated liquids have been presented. Abnormal rise of the dielectric constant in the mixture of rapeseed oil with methyl alcohol was observed. These results suggest the occurrence of a new phase transition apart from the one observed earlier in rapeseed oil [A.J. Rostocki, R. Wiśniewski and T. Wilczyńska, J. Mol. Liq., in press].